Articles & Case Studies

25 metres of solid concrete drilled out of deep drain

Posted: Wednesday 10th December 2008

Remote cutting system avoids renewal of residential drain

A UK regional groundworks contractor started work on a new residential development on a brownfield site. It was not realised that some of the existing foul drain connections on the site had not been capped, however and concrete from the new foundations found its way into the main 225mm clay drainpipe in the street and set, causing several major obstructions.

The contractor read in Drain Trader magazine about a similarly challenging removal job Tube Tech had carried out on a [deep drain that had been penetrated by a steel pile]* and contacted the company with his problem. Although originally contracted to clear a single known blockage, Tube Tech successfully cleared the drain run of three concrete obstructions, using a specially-designed and configured system, without any damage to the clay pipe. The contractor avoided having to dig up and re-lay 200 metres of drain - set in concrete with a larger surface water drain - and re-house the occupants of other properties still using the foul drain while the work was carried out.

Background

Formed in 1973, this building and civil engineering groundworks contractor now employs 150 people in the west of England. The range of contracts it undertakes includes: housing development - including road and sewer infrastructure, foundation and external works; commercial development - including major reinforced concrete structures and infrastructure works; local authority projects - including highway and bridge works, waterproofing and strengthening. The company's operations extend from Bristol along the M4 and M5 corridors, from Bridgend to Swindon and from Tewkesbury to Exeter.

Problem

The contractor had begun groundworks construction on a brownfield site in Bristol. When the site was cleared, not all entry points to the existing foul drains had been recorded and sealed. As the contractor began pouring concrete for house foundations, other properties in the road started experiencing problems with their drains. The drains were investigated with an inspection camera to ascertain the nature and extent of the problem and a large amount of concrete was found. Initially, only one obstruction was located - 17 metres long and 84 metres from the access point. Fortunately, the contractor found an article in Drain Trader magazine that reported on the successful removal by Tube Tech of a steel pile from a deep drain and contacted the company with his problem. Although Tube Tech was originally contracted to clear one obstruction, three partial or complete obstructions of set concrete, measuring 17, 8 and 4 metres in length, were eventually discovered in the 225mm i/d drain and removed completely.

Solution

Of the two manholes in the drain run, only one offered suitable access for a large pressure hose to be introduced into the drain and be able to move freely. In addition, it was preferable for the operators if they could work on the surface, rather than 3 metres below ground, which would require them to wear breathing apparatus and safety harnesses. Even so, the contractor had to reduce the access hole to make this possible. From the modified access hole, it was 84 metres in one direction to the first obstruction and 70 metres in the other direction to the second.

A specialised system was devised and assembled at Tube Tech's operations centre and then mobilised to site. A series of roller guides at the manhole ensured that the large pressure hose fed into the drain without snagging and helped reduce operator fatigue. Thanks to careful matching of the low-pressure, high-volume system with the right pump, all the concrete was removed without damaging the clay drain pipe; in fact it was not even scratched. This was achieved despite the fact that there was supposed to be no aggregate in the concrete obstructions, but the largest piece removed measured 1.5 metres in length - and was full of aggregate, which increased the challenge for the removal head.

Tube Tech Comment

Technical Sales Person, Eamonn O'Connor: "The customer was delighted - he had been faced with the prospect of replacing 200 metres of foul drain, and re-housing the occupants of the 50-60 properties connected to it while the work was carried out. Replacement would have also required the permission of the water authority, which was likely to be difficult to obtain. All in all, this job was just the kind of challenge we relish - and our reputation for solving such problems is growing all the time."